Next, go to All Apps and type in the keyword "Text Entry" to proceed to add Unikey support application to Ubuntu iBus percussion 13.10.
On the Text Entery interface , click on the "+" icon then enter the search box, Vietnamese (Unikey) to integrate Unikey into iBus and click the Add button to add it.
Finally just move Vietnamese (Unikey) with the arrow keys below the list so that Vietnamese (Unikey) ranks first, so Ubuntu will understand that Vietnamese (Unikey) is the default input method.